Bobcat 943 Hydro .......HELP

Just purchased the 943 to replace my L783 NH. Knew it had a issue when i bought it........ Brand new motor just built by a 40yr in biz builder. Motor runs perfect! Hydro is my issue. Full throttle the machine driving speed is 25% of what it should be. It drives straight, turn the same both ways. Bucket/lift work as they should, no issues with the lift. This machine has a "charge pump" that should put out about 400 psi ..... check it in the system and was getting about 100 -160 psi (idle/full throttle). I THOUGHT great it's a new charge pump and fairly cheap (300.00). Went to the hydro shop that i use (very good bunch of hydro guys and a large hydro shop) to buy a new pump. He said let me check your pump out real quick. 2 mins later he had it completely apart and said this pump is fine .... almost no wear at all ..... everything looks/feels great. He puts it back together and says " you need to be looking somewhere else". CRUD! (oh, never charged me anything and i was there to buy a pump) Where do i go from here? What should i test? How do i test it? i did buy some flat caps for testing. I have the factory service manual in hardback so i can answer some question if asked. Thanks for ANY and ALL help, S

Driving speed is directly connected to the stroke of your hydro pump swash plate. The more stroke, the higher the volume of flow (for speed). I am not sure what type of swash plate control you have, but if it is mechanical levers, you should check that and any linkage bushings, pins for wear or looseness. Check the simple stuff first before diving into your main pump.